Closing The Performance Gap Between <001>c Textured Pmn-pt ceramics And Single Crystals
Open Access
- Author:
- Poterala, Stephen F
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- None
- Committee Members:
- Gary Lynn Messing, Dissertation Advisor/Co-Advisor
Richard Joseph Meyer Jr., Dissertation Advisor/Co-Advisor
Susan E Trolier Mckinstry, Committee Member
James Hansell Adair, Committee Member
Clive A Randall, Committee Member
Michael T Lanagan, Committee Member - Keywords:
- Textured ceramic
PMN-PT
piezoelectric
texture
ceramic
templated grain growth - Abstract:
- <001>C textured PMN-PT ceramics fabricated by templated grain growth (TGG) show more than twice the piezoelectric response of conventional PZT-based ceramic materials, and show great promise for a large number of transducer applications. Over the past decade, numerous researchers have greatly advanced the processing and performance of these materials. However, the best textured PMN-PT ceramics show properties only halfway between those of ceramics and <001>C oriented crystals. In this work, long-standing problems in processing of textured PMN-PT ceramics are investigated in order to close the performance gap between textured ceramic and single crystal materials. First, novel plate-like 0.4(Na1/2Bi1/2)TiO3-0.6PbTiO3 templates were synthesized in order to avoid deleterious effects of BaTiO3 and SrTiO3 on texture development and properties. To produce these particles, topochemical conversion of PbBi4Ti4O15 to PbTiO3 was studied in comparison to reactions yielding BaTiO3 and NaNbO3 microplatelet templates. Conversion was found to occur via multiple nucleation and growth of the perovskite phase, followed by recrystallization to eliminate microstructure damage. Formation of phase-pure perovskite templates was aided by partial solid solution of Na+ and Bi3+ on the perovskite A-site of PbTiO3. Undoped <001>C textured PMN-PT fabricated with these templates has both high density (~99%) and high texture quality (f = 92%), and shows higher electromechanical coupling (k33 = 0.83) than previous textured ceramics. Complete sets of electromechanical properties of textured PMN-PT are reported for the first time for both undoped and Mn2+ doped compositions. Both materials have enhanced coupling coefficients in the 33 and 31 modes, despite having crystal-like mechanical properties only in the texture (33) direction. In addition, the dielectric properties of both materials remain ceramic-like. As a result, enhancement of d33 is associated with increases in sE33 and k33, while enhancement of d31 is associated mainly with an increase in k31. Rayleigh analysis of textured PMN-PT ceramics indicates that <001>C texture strongly reduces extrinsic contributions to ferroelectric properties, and this effect may partially explain the gap between textured ceramic and crystal performance. Because extrinsic response is already limited in Mn2+ doped textured ceramics, it is likely that acceptor doped textured ceramics may perform similarly to doped single crystals. The scalability and flexibility of textured PMN-PT fabrication is demonstrated by successful fabrication of 5 cm cylindrical transducer elements with radial <001>C texture. Spatial control of the texture orientation allows fabrication of omni-directional transducers from monolithic textured ceramics, whereas use of crystal requires a segmented design approach. In order to further improve the properties of <001>C textured PMN-PT, new approaches for particle alignment were investigated. To avoid fundamental limits on shear-based methods such as tape casting, dynamic magnetic alignment (MA) was used in conjunction with slip casting and TGG methods. Using this approach we demonstrate narrow grain orientation distributions (FWHM ~7°) are attainable at low field levels (2.2 T) in a permanent magnet array. Texture qualities in these ceramics were limited by morphologic defects (grain boundaries or domain structure) in the template particles used, and this method may be further optimized to yield substantially narrower grain orientation distributions.